mytest > help > Part 2. MM4XL Tools > 1. Strategic Tools > Risk Analyst > 4. Functions > 3. Distribution Functions > mmNEGBIN(Failures, Successes)

Risk Analyst

mmNEGBIN(Failures, Successes)

Example

=mmNEGBIN(1, 0.5) can equal 1.

Application

Also called the Pascal variate, this function returns the number of trials needed to reach a given number of successes according to a given success rate. For example, you need to find 10 people with excellent reflexes, and you know the probability that a candidate has these qualifications is 30%. mmNEGBIN(10, 0.3) calculates the probability that you will interview a certain number of unqualified candidates before finding all 10 qualified candidates. It is also used to model the distribution of cavities in a group of dental patients.

How to use

This function returns the number of trials before reaching a certain number of successes. Say that we are planning to use outdoor advertising for our store and we are wondering about the visits to the store that billboards can generate, which impacts on sales. From a survey study we know that 30% of the 25,000 pedestrians exposed to the billboard each day notice it, and 6.5% of the 30% enter the store. The formula below can help to model the required number of pedestrians exposed to the billboard in order to obtain 10 visits:

=mmNEGBIN(10, 0.0195)

Copy the formula above in 100 cells. You will find that the most likely value is around 450, which means that of every 450 people who notice the billboard, 10 enter in the store.

Technical profile

Type Discrete distribution.
Syntax =mmNEGBIN(Failures, Successes)
Domain  Monte Carlo Simulation Software: Management Process Risk Analysis
Mode If a = integer then = a <= x <= a+1
Otherwise = a+1
a =  Monte Carlo Simulation Software: Management Process Risk Analysis
Parameters Failures = 0 <= x < Infinity, x = an integer
Successes = 0 < p < 1
Remarks If any argument is nonnumeric mmNEGBIN returns the #VALUE! error value.
Relationships It is related to the Geometric variate. It is related to the Poisson variate as Failures tends to infinity and Successes tends to 1.
Graphs
mmNEGBIN(1, 0.5) mmNEGBIN(10, 0.5)
 Monte Carlo Simulation Software: Management Process Risk Analysis  Monte Carlo Simulation Software: Management Process Risk Analysis
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